Various fluids, such as whole blood or various other biological fluids, may be separated into their constituent parts, also referred to as fractions or phases. For example, whole blood samples may include a plurality of constituents that may be separated by density in a device such as a centrifuge. The whole blood sample may be placed in a test tube, or other similar device, which is then spun in a centrifuge. In the centrifuge the whole blood is separated into different fractions depending upon the density of that fraction. The centrifugal force separates the blood or other sample into different fractions. In addition, various elements may be added to the test tube to create more than two fractions. In particular, commonly used gels may be used to divide the whole blood into a plurality of different fractions which may include fractions such as platelets, red blood cells, and plasma. Various other biological fluids may be separated as well. For example, nucleated cells may be separated and extracted from bone marrow or adipose tissue sample.
Many of these systems, however, do not provide a simple or efficient method to extract any more than one fraction and, especially, a fraction other than the top fraction. The top fraction of whole blood is plasma, or other blood constituents suspended in plasma. Thus, to extract other fractions the plasma fraction must either be removed for further extracting procedures or spun again to obtain the constituents suspended in this plasma. It is difficult to pierce the top fraction without commingling the sample. Accordingly, obtaining the other fractions is difficult with commonly known systems.
Other systems have attempted to alleviate this problem by providing a float or other device that is disposed within the sample at the interfaces of the different fractions during the centrifuge process. Nevertheless, these systems still do not allow a simple way to remove the different fractions without remixing the sample fractions. In addition, many of the systems do not allow an easy and reproducible method to remove the desired sample fraction.
Therefore, it is desired to provide a device to allow for the easy and reproducible removal of a particular fraction which does not happen to be the top fraction of a sample. It is desired to remove the required sample without mixing the different fractions during the extraction process. In addition, it is desired to provide a device which allows for a consistent extraction which includes known volumes or concentration of the fraction elements. Moreover, it is desired to separate and concentrate a selected fraction with one centrifugation step.